command/queue: better error message for open-ended range with "move"

The "move" command doesn't allow open-ended ranges because they don't
make a lot of sense; moving an open-ended range is only possible if
the destination index is before the range, and in that case, the
client should be well aware how many songs there are.

Closes https://github.com/MusicPlayerDaemon/MPD/pull/1057

src/command/QueueCommands.cxx

@@ -326,6 +326,11 @@ CommandResult
 handle_move(Client &client, Request args, [[maybe_unused]] Response &r)
 {
 	RangeArg range = args.ParseRange(0);
+	if (range.IsOpenEnded()) {
+		r.Error(ACK_ERROR_ARG, "Open-ended range not supported");
+		return CommandResult::ERROR;
+	}
+
 	int to = args.ParseInt(1);
 	client.GetPartition().MoveRange(range.start, range.end, to);
 	return CommandResult::OK;